The present invention relates to the field of kneading machines for food products and particularly (but not exclusively) to machines for preparing flour-based mixtures, of the type comprising:
a kneading bowl, defining a channel having a loading area for the product to be kneaded and an unloading area for the kneaded product, PA1 a plurality of kneading tools arranged within said channel and rotatable around axes which are preferably substantially vertical, and PA1 means for advancing the product through said channel from said loading area to said unloading area. PA1 a kneading bowl, defining a channel having a loading area for the product to be kneaded and an unloading area for the kneaded product, PA1 a plurality of kneading tools arranged in said channel and rotatable around substantially vertical axes, and PA1 means for advancing the product in said channel from said loading area to said unloading area, wherein:
Kneading machines of the above indicated type are disclosed for example in European patent EP-B-0 469 500 of the same Applicant, in the corresponding U.S. Pat. No. 5,312,183 and in European patent application EP-A-0 554 513 also of the same Applicant.
According to the most conventional art, the kneading machines for food products include a container in the form of a rotary bowl in which the ingredients of the mixture are placed and which then brings the various portions of the mixture up to the kneading tool during kneading. Machines of this type have kneading tools of various configurations. A particularly advantageous version is a so-called "helical" machine, that is, a machine with a helical kneading tool constituted by a bar with a circular cross-section arranged helicoidally around a theoretic ideal cylinder. These machines produce very good results from the point of view of the quality of the mixture, they perform the kneading cycle fairly quickly, and they can be used to work on different mixtures, their operating characteristics being adapted from time to time to the type of mixture being kneaded.
Machines with rotary bowls have the disadvantage, however, that their operating cycles are discontinuous. In other words, each kneading cycle includes the loading of the bowl with the ingredients of the mixture and finishes with the discharge of the mixture produced from the bowl. Only after the discharge stage is completed can the bowl be refilled with the ingredients necessary to make a fresh mixture. Moreover, for large-scale commercial production, kneading bowls of ever-increasing size tend to be used in order to produce the largest possible batch of mixture in each kneading cycle. At the end of the kneading cycle, the mixture is discharged from the bowl and sent to the user machines, for example, a chopping machine or a moulding machine. In the case of a mixture-containing yeast, the first portion of mixture discharged from the bowl will reach the user machine considerably in advance of the last portion of the mixture, and this results in a different rising time and, eventually, to non-uniform characteristics of the final product.
Naturally, this disadvantage could be avoided by the use of kneading machines which can work continuously. In fact, another conventional technique uses a continuous-flow kneading machine which comprises, essentially, a tubular element containing an Archimedean screw shaft or the like which advances the product along the tubular element and at the same time forms the mixture. However, these known kneading machines of the continuous-flow type cannot produce a mixture of a quality comparable to that which can be produced by a machine with a rotary bowl, particularly a helical machine.
In European patent EP-B-0 469 500, the Applicant has proposed a kneading machine of the type indicated at the beginning of the present description which is able to work continuously and does not have the drawbacks typical of the conventional continuous kneading machines which have been mentioned above. According to this proposal, a kneading machine for food products comprises a container constituted by a straight channel-shaped element along which the mixture being formed is advanced and which has an input end for admitting the product to be kneaded and an output end for discharging the mixture produced. Along the channel-shaped element there are distributed many kneading tools rotatable around vertical axes and preferably of helical shape. The input end of the channel-shaped element is fed alternatively by two mixing units with a sequence of batches of mixed product, so as to form a continuous elongated mass of product which advances along the channel-shaped element meeting thereby in sequence the various kneading tools which provide the kneading thereof. Each of the pre-mixing units arranged upstream of the channel-shaped element is provided for preparing batches of pre-mixed product with precisely weighed quantities of predetermined ingredients. By pre-mixed product, it is meant herein a mixture of the various ingredients having a mass of uniform composition in which however the kneading stage proper, in Which formation of gluten takes place, has not yet commenced, this stage being performed in the channel-shaped element. Due to the above mentioned arrangement, the elongated mass of dough coming out of the machine which has been previously proposed by the Applicant has a uniform composition and the adjustment of the machine for production of a dough according to a different recipe is rapid and without difficulty. Therefore, the continuous kneading machine previously proposed by the Applicant does not have the drawbacks typical of the conventional continuous machines. Furthermore, the use of kneading tools of the helical type enables all the advantages typical of the conventional helical kneading machines, with respect to rapidity and quality of the kneading action, to be retained.
Also with reference to the continuous kneading machine previously proposed by the Applicant, in order to control precisely the advancement of the elongated mass of mixture along the channel element, there are provided means to create a cyclic relative movement between the channel element and the group of kneading tools. This cyclic movement includes a first step of horizontal movement (of the channel element with respect to the kneading tools) against the flow of the product, a second descending step, a third step of horizontal movement in the direction of flow of the product and a fourth climbing step. This relative movement may be provided as a movement of the channel element with respect to the kneading tools, or as a movement of the structure carrying all the kneading tools with respect to the channel element. At any rate, the need of providing said relative movement gives raise to a relatively complicated and costly structure, which can be a source of vibrations and problems in operation because of the relatively high weight of the various moving unbalanced masses.
It is also to be noted that the Applicant, in the endeavour to further improve the above described kneading machine, has proposed in its European patent application EP-A-0 554 513 an improved version of this machine which is provided inside of the channel element with a number of counter member walls, rigidly connected to the structure carrying the kneading tools, and each arranged immediately after a respective kneading tool (with reference to the direction of flow of the product), so as to avoid that while a portion of the elongated mass is worked by the kneading tool which has intercepted it, a portion of the dough is thrown by centrifugal force away from the tool, thus escaping to the kneading action.
This improved machine has improved the ability of controlling the kneading process, but has not eliminated the need of using the above described complicated structure in order to provide the relative movement between the channel element and the kneading tools. Also this machine keeps the drawback that during the step of the above described cyclic movement in which the bottom of the channel element is more spaced apart from the kneading tools, the kneading action is interrupted.
SU-A-1.414.659 discloses a machine of the type indicated at the beginning of the present description, belonging to a different field (building mixtures). This machine would be completely unuseful for preparing food admixtures, due to a number of reasons. Firstly, in this known machine the circumferential inner wall of the endless channel rotates relative to the bottom wall of the channel, thus originating the danger of a leakage of product through the gap between said walls. Moreover, which is more important, the channel obstructing walls, in this known machine, are spaced apart fromthe respective mixing tools and have a planar configuration, which would prevent, in case of processing a food admixture, a product of high quality to be obtained.